One type of milkweed that can have a negative impact on monarch butterflies is tropical milkweed (Asclepias curassavica). While this plant may seem beautiful and harmless, it can actually interfere with monarch migration and reproduction.
One way in which tropical milkweed can harm monarch butterflies is by disrupting their natural migration patterns. Monarchs are known for their incredible long-distance migrations, with some individuals traveling thousands of miles to reach their wintering grounds in Mexico or California. However, the presence of tropical milkweed in northern areas can confuse monarchs into thinking that it is still breeding season, leading them to stay and reproduce instead of continuing their journey.
This confusion is caused by the extended growing season of tropical milkweed in comparison to native milkweed species. In northern regions, native milkweed species typically die off in the fall, signaling to monarchs that it is time to migrate. However, tropical milkweed continues to grow and flower later into the year, providing a false signal to monarchs that there is still food available for their caterpillars. This can result in monarchs laying eggs and breeding at a time when they should be focused on migrating.
The consequences of this disruption in migration can be detrimental to monarch populations. Monarchs that breed on tropical milkweed in the fall may not have enough time to complete their life cycle before winter arrives. As a result, their offspring may not be able to make the long journey to the wintering grounds, leading to a decline in population numbers.
Another concern with tropical milkweed is its potential to harbor a parasite called Ophryocystis elektroscirrha (OE). This parasite can infect monarch butterflies and weaken their immune systems, making them more susceptible to disease and reducing their overall fitness. Tropical milkweed, being a non-native species, may have a higher prevalence of this parasite compared to native milkweed species. When monarchs repeatedly breed on tropical milkweed, the risk of infection and the spread of OE can increase.
To mitigate the negative impacts of tropical milkweed on monarch butterflies, it is recommended to limit its use in areas where monarchs migrate through or breed. Instead, consider planting native milkweed species that naturally die back in the fall, signaling to monarchs that it is time to migrate. By providing the right cues and conditions for monarchs to undertake their incredible migration, we can help support their populations and ensure their long-term survival.
While tropical milkweed may be visually appealing, its presence can disrupt monarch migration and reproduction. By understanding the potential harm it can cause and making informed choices about the plants we grow, we can play a role in conserving monarch butterflies and their incredible migratory journeys.
